Arrangement for modulating high frequency oscillations



set 1938- H. E. VON COLLAS 2,130,381

ARRANGEMENT FOR MODULATING HIGH FREQUENCY OSCILLATIONS Filed Aug. 18, 1936 2 Sheets-Sheet l pt; 20, 11938. H. E. VON cbLLAs 2,130,381

ARRANGEMENT FOR MODULATING HIGH FREQUENCY OSCILLATIONS Filed Aug. 18, 1956 2 Sheets-Sheet 2 J 57' 1 7i- 507i YQMJW 4 Patented Sept. 20, 1938 UiTED STATES PATENT OFFICE many, assignor to C. Lorenz Aktiengescllschaft, Berlin-Tempelhof, Germany, a company Application August 18, 1936, Serial No. 96,568

In Germany 3 Claims.

The modulation of high frequency oscillations, especially of ultra-short waves, requires special measures to be adopted because the oscillation generators employed in ultra-short wave systems 5 tend to vary in frequency under the influence of the variations ordinarily applied to produce modulation. One type of oscillation generator used for ultra-short waves is the kind operating with the aid of Habann tubes. A Habann tube is a magnetron which has a central cathode and concentrically-surrounding this cathode a cylindrical anode split into two electrically separate half cylinders. When used for generating oscillations each half of the anode acts asa control electrode to regulate the fiow of electrons to the other half anode. The frequency of these generators varies with variations of the magnetic field, and also with Variations of the anode potential. Moreover the required power input is very great if the modulation is effected in the magnetic field of the Habann tubes. It may be thought that undesired frequency variation mightbe obviated by modulating in the magnetic field and with the aid of the anode potential at the same time, but in any case there will still be the drawback of the power input being very great.

Other oscillation generators, such for example as those operating in brake field connection also exhibit this tendency to vary in frequency when modulated in the ordinary manner. In the case of these brake-field tubes it is well known to avoid frequency variations by providing a variable oscillation absorption device in a circuit in which unmodulated oscillations occur, such device being varied in the rhythm of the modulating frequency.

The invention described hereinafter employs this absorption principle of modulation just mentioned, but makes use of a magnetron tube for the absorbing device, the preferred type being a Habann tube such as described in the preceding discussion of oscillators. Although the modulating device of the present invention is a magnetron, its application is not restricted to oscillators of the magnetron type but it is applicable to oscillation generators of any kind and with a good effect in each case.

Some embodiments of the invention are disclosed in the following description, reference being had to the accompanying drawings in which these embodiments are illustrated by wiring diagrams.

Fig. 1 shows an example of a modulating ar rangement as provided by the invention. Fig. 2 represents a second example of such an arrangement. Figs. 3, 4, 5, 7 each show a transmitter August 19, 1935 which has a modulating arrangement of the land illustrated in Fig. 1. Fig. 6 is a diagram relating to the mode of action of such a modulating arrangement. Fig. 8 shows a transmitter fitted with a modulating arrangement embodying a slight modification of the arrangement represented in Fig. 2.

Like parts in the several views are denoted by the same reference characters.

The modulating arrangement according to Fig. 1 has a Habann tube H, the anode consisting of two cylinder portions A. The heating filament or cathode K is located in the axis of the cylinder A, A. Two magnets M are arranged to produce a magnetic field whose lines of force extend along the axis of the cylinder A, A. These magnets are shown as displaced by from their actual position. A voltage source Bm serves to feed them. L denotes a coil of the oscillatory circuit of the tube H. Dr indicates a choke over which the continuous anode voltage is conveyed from a bat tery Ba to the anode members A. Over a transformer T the modulating frequency, such as speech, telegraphic signals or picture frequency, is also conducted to the anode circuit. The modulation is effected either by varying the voltage connected to the anode members A or with the aid of a grid disposed in tube H, such as grid G shown in Fig. '7.

The modulating arrangement according to Fig. 2 has a magnetron diode P. Here the modulation is likewise accomplished by varying the anode voltage.

Instead of a magnetron diode such as P a magnetron triode Q may be provided, as represented in Fig. 8. The grid G of the tube Q serves to effect the modulation, as is the case also with the arrangement illustrated in Fig. 7.

With these tubes H, P, or Q the magnetic field produced by the magnets M causes the electrons emitted by the filament K to follow a closed or circular path from this filament so as to return to this filament. The conditions are here preferably so chosen that the rotational frequency, that is, the number of revolutions of an electron, is brought to resonance, or nearly so, with the modulated frequency, and are also so chosen that the anode voltage is so low and that further the dimensions are so great that no anode current or only a very small one shall flow during the state of rest.

In the arrangements shown in Figs. 1 and 2 a high frequency source is coupled to L and LC, respectively, in substantially the same manner as in the arrangement shown in Fig. 4.

' of this tube are denoted by M.

The transmitter according to Fig. 3 is designed to operate with the aid of a feed-back connection over the internal valve capacity. The oscillatory tube of this transmitter is designated R. Connected to the grid and anode of the tube R is an oscillatory circuit which comprises an inductance LI and a capacity CI. The grid of the tube R is blocked against continuous voltage by means of a condenser C2. A choke Drl and resistance WI constitute a grid leak. A dipole Di is coupled to the inductance Ll by an inductance L2. The arrangement as thus far described is known and serves to generate very short oscillations. To the condenser Cl a modulating arrangement of the kind shown in Fig. 1 is connected, that is, a modulating arrangement which comprises a Habann tube H having the two anode members A, the heating filament K, the magnets M, the voltage source Bm for feeding these, the voltage source Ba for supplying direct voltage to the anodes, the choke DrZ through which battery Ba is connected to the anode members A, and the transformer T through which the modulating frequency is conveyed to the anode circuit. A symmetrical circuit having two Lecher wires S! S2 is connected to the .anode members A. Condenser Cl is located in a potential node of the wires S E, SE.

A transmitter of the kind represented in Fig. 3 is shown also in Fig. 4. Here however a different mode of coupling the modulating arrangement to the transmitter is disclosed.

Fig. 5 shows a mode of coupling the modulating arrangement to a Habann tube transmitter whose oscillatory tube is designated H. The magnets The battery for feeding the magnets M is designated Bm'. The oscillation generating portion of this arrangement, which serves to produce ultra-short waves, is in itself not novel. The modulating tube H may be disposed directly in the Lecher system of the transmitter, as will appear from Fig. 5.

Figs. 3 to 5 thus by way of example illustrate some possibilities of coupling to a transmitter a modulating arrangement of the type shown in r Fig. l. The function of the modulating arrangement is very eifectual especially if the rotational frequency of the electrons is in resonance, or nearly so, with the transmitter wave and if the anode potential is made so low that no anode current or only a very small one shall flow.

The static modulation characteristic here concerned is represented in Fig. 6. The working point is determined by the anode bias Ba. Jw denotes the high frequency current, Ua the anode potential. By choosing both the anode potential and the magnetic field of the modulating arrangement in the described manner a very high degree of modulation is obtained. The main advantage of the novel arrangement is that with a very small power input a sufiicient modulation of the high frequency oscillations is ensured without entailing a detrimental frequency variation.

The arrangement shown in Fig. 7 is the same as that represented in Fig. 3, except that the Habann tube H in the case of Fig. '7 has a grid G, as stated before, the modulation being effected here with the aid of this grid.

The arrangement according to Fig. 8 is likewise quite similar to that illustrated in Fig. 3. The difference between the two is that the before mentioned magnetron triode Q is provided instead of the Habann tube H, the modulation being effected with the aid of the grid G of this tube Q. This grid G is coaxially positioned with respect to the cathode K and is supplied with modulation voltages by means of transformer T.

Thus, in the arrangements shown in Figs. 7 and 8 the modulation is effected by varying the grid potential, whilst in the case of Figs. 3, 4, 5 it is performed by varying the anode potential.

It is however possible also to modulate both grid and anode potential in order to compensate .for any slight frequency variations that may still occur in consequence of any particulars of the circuit arrangement.

The examples here described show that the invention is not restricted to the use of Habann tubes but may be effected also by means of magnetron diodes or magnetron triodes, although preferably Habann tubes should be employed.

What is claimed is:

1. In an arrangement for modulating high frequency oscillations, a high frequency oscillation circuit, means for varying the leakage of said high frequency oscillation circuit, said means including an electron tube having a subdivided anode, the po-rtions of which are included in the oscillation circuit, and means for producing a magnetic field to control the discharge space of said tube, said magnetic field being such that the natural rotational frequency of the electrons in said tube corresponds to the frequency of the oscillations to be modulated.

2.An arrangement according to claim 1 and in which the oscillation circuit is symmetrically arranged with respect to the portions of the anode.

3. An arrangement according to claim 1 and in which said electron tube has a grid, and means provided for conveying the modulating frequency to said grid.

HANS EBERHARD v. COLLAS. 

